U.S. patent application number 15/699389 was filed with the patent office on 2019-03-14 for endovascular device configured for controlled shape memory deployment in a body vessel.
This patent application is currently assigned to Cook Medical Technologies LLC. The applicant listed for this patent is Cook Medical Technologies LLC. Invention is credited to Woong Kim.
Application Number | 20190076583 15/699389 |
Document ID | / |
Family ID | 63452584 |
Filed Date | 2019-03-14 |
United States Patent
Application |
20190076583 |
Kind Code |
A1 |
Kim; Woong |
March 14, 2019 |
ENDOVASCULAR DEVICE CONFIGURED FOR CONTROLLED SHAPE MEMORY
DEPLOYMENT IN A BODY VESSEL
Abstract
A method of controllably deploying an endovascular device
comprises delivering, into a body vessel, a Nitinol structural
element comprising a variable austenite finish temperature
A.sub.f(x) along a predetermined length (L) thereof, where
0<x.ltoreq.L. The variable austenite finish temperature
A.sub.f(x) increases or decreases monotonically as a function of x
and lies above body temperature at any location along the
predetermined length of the Nitinol structural element. During
and/or after delivery into the body vessel, the Nitinol structural
element is heated above body temperature. As a temperature of the
Nitinol structural element reaches A.sub.f(x) at each location
along the predetermined length, the Nitinol structural element
recovers a pre-set shape at the respective location, and the
endovascular device is controllably deployed.
Inventors: |
Kim; Woong; (West Lafayette,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cook Medical Technologies LLC |
Bloomington |
IN |
US |
|
|
Assignee: |
Cook Medical Technologies
LLC
Bloomington
IN
|
Family ID: |
63452584 |
Appl. No.: |
15/699389 |
Filed: |
September 8, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 31/022 20130101;
A61F 2/0031 20130101; A61L 2400/16 20130101; A61F 2/91 20130101;
A61F 2/848 20130101; A61F 2/88 20130101; A61F 2220/0016 20130101;
A61F 2250/0018 20130101; A61F 2002/8483 20130101; A61F 2250/0042
20130101; A61L 31/14 20130101; A61F 2210/0014 20130101; A61F
2210/0033 20130101; A61F 2210/0023 20130101; A61F 2/01 20130101;
A61F 2210/0038 20130101; A61F 2002/018 20130101; A61F 2/95
20130101; A61F 2002/016 20130101 |
International
Class: |
A61L 31/02 20060101
A61L031/02; A61L 31/14 20060101 A61L031/14 |
Claims
1. An endovascular device configured for controlled deployment in a
body vessel, the endovascular device comprising: a Nitinol
structural element comprising a variable austenite finish
temperature A.sub.f(x) along a predetermined length (L) thereof,
where 0<x.ltoreq.L, the variable austenite finish temperature
A.sub.f(x) monotonically increasing or decreasing as a function of
x and being above body temperature at any location along the
predetermined length, the endovascular device thereby being
configured for controlled deployment within a body vessel.
2. The endovascular device of claim 1, wherein the endovascular
device comprises a fully deployed configuration after being heated
to a temperature at or above a highest value of the variable
austenite finish temperature A.sub.f(x).
3. The endovascular device of claim 1, wherein the Nitinol
structural element further comprises a variable austenite start
temperature A.sub.s(x) above body temperature at any location along
the predetermined length.
4. The endovascular device of claim 3, wherein the variable
austenite start temperature A.sub.s(x) monotonically increases or
decreases as a function of x.
5. The endovascular device of claim 1, wherein the Nitinol
structural element comprises from about 50 at. % to about 52 at. %
nickel.
6. The endovascular device of claim 1 being a stent, filter, cage,
fastener, ratchet or anchor.
7. A method of controllably deploying an endovascular device, the
method comprising: delivering a Nitinol structural element into a
body vessel, the Nitinol structural element comprising a variable
austenite finish temperature A.sub.f(x) along a predetermined
length (L) thereof, where 0<x.ltoreq.L, the variable austenite
finish temperature A.sub.f(x) increasing or decreasing
monotonically as a function of x and being above body temperature
at any location along the predetermined length; and heating the
Nitinol structural element above body temperature, wherein, as a
temperature of the Nitinol structural element reaches A.sub.f(x) at
each location along the predetermined length during the heating,
the Nitinol structural element recovers a pre-set shape at the
respective location and the endovascular device is controllably
deployed.
8. The method of claim 7, wherein the Nitinol structural element
further comprises a variable austenite start temperature A.sub.s(x)
having a value above body temperature at any location along the
predetermined length.
9. The method of claim 8, wherein the variable austenite start
temperature A.sub.s(x) monotonically increases or decreases as a
function of x.
10. The method of claim 7, wherein the heating is carried out
uniformly along the predetermined length, the temperature of the
Nitinol structural element being uniform to within .+-.1.degree.
C.
11. The method of claim 7, wherein the heating is carried out by a
heat source selected from the group consisting of: induction heater
and resistive heater.
12. The method of claim 7, wherein a martensite start temperature
of the Nitinol structural element is below body temperature, the
deployed configuration remaining stable upon cooling after
completion of the heating.
13. The method of claim 7, wherein the Nitinol structural element
comprises a wire, rod, tube, or strip, and wherein the endovascular
device comprises a stent, filter, cage, fastener, ratchet, or
anchor.
14. The method of claim 7, wherein the Nitinol structural element
comprises from about 50 at. % to about 52 at. % nickel.
15. A method of heat setting an endovascular device for controlled
deployment in a body vessel, the method comprising: securing a
Nitinol structural element having a first end and a second end in a
predetermined configuration; heating the first end of the Nitinol
structural element, the second end of the Nitinol structural
element not being heated; and after a predetermined time duration,
halting the heating, wherein, during the heating, a temperature of
the Nitinol structural element is increased along a length thereof
by thermal conduction from the first end, thereby producing a
temperature gradient between the first end and the second end,
wherein, after the heating, the Nitinol structural element
comprises a variable austenite finish temperature A.sub.f(x) along
the length (L) between the first end and the second end, where
0<x.ltoreq.L, the variable austenite finish temperature
A.sub.f(x) increasing or decreasing monotonically as a function of
x and being above body temperature at any location along the
length, the endovascular device thereby being configured for
controlled deployment within a body vessel.
16. The method of claim 15, wherein the Nitinol structural element
is at least partially covered by an insulation layer between the
first end and the second end during the heating.
17. The method of claim 15, wherein, after the heating, the Nitinol
structural element comprises a variable austenite finish
temperature A.sub.s(x) along the length between the first end and
the second end, where 0<x.ltoreq.L, the variable austenite start
temperature A.sub.s(x) increasing or decreasing monotonically as a
function of x and being above body temperature at any location
along the length.
18. The method of claim 15, further comprising, during the heating,
cooling the second end of the Nitinol structural element to
modulate the temperature gradient.
19. The method of claim 15, wherein the heating is carried out at a
heat setting temperature from about 350.degree. C. to about
550.degree. C. using a concentrated heat source.
20. The method of claim 15, wherein halting the heating comprises
quenching, the Nitinol structural element being exposed to a
cooling fluid.
Description
TECHNICAL FIELD
[0001] The present disclosure is related generally to endovascular
devices and more specifically to an endovascular device comprising
a nickel-titanium shape memory alloy ("Nitinol").
BACKGROUND
[0002] Superelastic deployment of Nitinol-based endovascular
devices is widely used to implant stents, filters and other devices
into blood vessels. Such devices are typically heat set to a single
static shape (e.g., a radially-expanded shape in the case of a
stent) that can be recovered spontaneously upon removal of a
constraining force, such as an overlying tubular sheath, after
delivery of the device into a target vessel. Such nitinol-based
devices may have austenite finish temperatures (A.sub.f) below body
temperature to ensure that removal of the constraining force, once
the device is delivered into the vessel, is sufficient to induce
the transformation from martensite to austenite that is needed for
shape recovery. Shape memory deployment of endovascular devices,
where austenite finish temperatures may be at or above body
temperature and heating is employed to induce shape recovery, is
not widely used for Nitinol-based endovascular devices due to a
number of practical challenges, such as the difficulty of
controlling temperature in situ. Furthermore, current Nitinol-based
endovascular devices utilize a bimodal approach of deformation and
recovery to a preset shape defined by a single A.sub.f
temperature.
BRIEF SUMMARY
[0003] An endovascular device configured for controlled deployment
in a body vessel comprises a Nitinol structural element having a
variable austenite finish temperature A.sub.f(x) along a
predetermined length (L) thereof, where 0<x.ltoreq.L. The
variable austenite finish temperature A.sub.f(x) monotonically
increases or decreases as a function of x and lies above body
temperature at any location along the predetermined length.
Accordingly, the endovascular device is configured for controlled
deployment within a body vessel.
[0004] A method of controllably deploying an endovascular device
comprises delivering, into a body vessel, a Nitinol structural
element comprising a variable austenite finish temperature
A.sub.f(x) along a predetermined length (L) thereof, where
0<x.ltoreq.L. The variable austenite finish temperature
A.sub.f(x) increases or decreases monotonically as a function of x
and lies above body temperature at any location along the
predetermined length. After delivery into the body vessel, the
Nitinol structural element is heated above body temperature. As the
temperature of the Nitinol structural element reaches A.sub.f(x) at
each location x along the predetermined length, the Nitinol
structural element recovers a pre-set shape at the respective
location, and the endovascular device is controllably deployed.
[0005] A method of heat setting an endovascular device for
controlled deployment in a body vessel comprises securing a Nitinol
structural element having a first end and a second end in a
predetermined configuration and heating the first end of the
Nitinol structural element. The second end of the Nitinol
structural element does not undergo heating. During the heating of
the first end, the temperature of the Nitinol structural element is
increased along a length thereof by thermal conduction, producing a
temperature gradient between the first end and the second end.
After a predetermined time duration, the heating is halted, and the
Nitinol structural element comprises a variable austenite finish
temperature A.sub.f(x) along the length (L) between the first end
and the second end, where 0<x.ltoreq.L. The variable austenite
finish temperature A.sub.f(x) increases or decreases monotonically
as a function of x and lies above body temperature at any location
along the length. Thus, the endovascular device is configured for
controlled deployment within a body vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates controlled deployment of an exemplary
endovascular device comprising a Nitinol structural element. The
endovascular device is shown at the top of FIG. 1 in a delivery
configuration and in the bottom-most schematic in a fully deployed
configuration after heating. In between, the endovascular device is
shown undergoing controlled deployment as a function of
temperature.
[0007] FIG. 2 is a schematic of an induction triggered active
anchoring system (ITAAS) configured to pierce a vessel wall and
coil up, utilizing the controlled deployment process described
herein.
[0008] FIG. 3 shows a heat setting simulation of a Nitinol wire of
0.48 mm in diameter heated at the first end (center of coil) to
500.degree. C. using a concentrated heat source. The coil is
surrounded by air at 22.degree. C.
DETAILED DESCRIPTION
[0009] The present disclosure describes an endovascular device that
can be delivered into a body vessel and can spontaneously
recover--at a controlled rate--a deployed configuration when
heated, preferably by a remote heat source. The method is enabled
by the use of a Nitinol structural element having an austenite
finish temperature (A.sub.f) above body temperature that varies
monotonically along a length of the element. The Nitinol structural
element may take the form of a wire or another shape, such as a
rod, tube or strip, preferably having an elongated geometry.
[0010] The Nitinol structural element comprises a nickel-titanium
alloy that exhibits shape memory behavior. In other words, the
nickel-titanium alloy can undergo a phase transformation that
allows it to "remember" and return to a previous shape or
configuration. More specifically, the nickel-titanium alloy can
transform between a lower temperature phase (e.g., martensite) and
a higher temperature phase (e.g., austenite) in order to effect
shape or strain recovery. As would be known by the skilled artisan,
austenite is characteristically the stronger phase, and martensite
may be deformed up to a recoverable strain of about 8%. Strain
introduced in the alloy in the martensitic phase may be
substantially recovered upon completion of a reverse phase
transformation to austenite, allowing the alloy to return to the
previous shape. The temperature at which the strain recovery occurs
may depend on the phase transformation temperatures of the
nickel-titanium alloy, as discussed further below. The strain
recovery can be driven by the application and removal of stress
(superelastic effect) and/or by a change in temperature (shape
memory effect), as in the present disclosure. Such alloys are
commonly referred to as Nitinol or Nitinol alloys, and they are
typically near-equiatomic in composition.
[0011] The method may be understood in view of the schematics of
FIG. 1, which illustrate the controlled deployment of an exemplary
endovascular device 100 comprising a Nitinol structural element
(which is a Nitinol wire in this example) 102 during heating. The
endovascular device 100 is shown at the top of FIG. 1 in a delivery
configuration and in the bottom-most schematic in a fully deployed
configuration after being heated to 60.degree. C. In between, the
endovascular device 100 is shown undergoing controlled deployment
as the temperature of the Nitinol structural element 102 is
increased above body temperature (37.degree. C.). The endovascular
device 100 may comprise a stent, filter, cage, fastener, ratchet,
anchor or another device.
[0012] The method entails delivering the Nitinol structural element
102 to a predetermined location in a body vessel. During delivery,
the Nitinol structural element 102 is in an undeployed or delivery
configuration which may be, for example, a substantially straight
configuration that can be readily maneuvered through the vessel. As
a consequence of the heat setting process described below, the
Nitinol structural element 102 has a variable austenite finish
temperature A.sub.f(x) along a predetermined length (L) thereof,
where 0<x.ltoreq.L. The variable austenite finish temperature
A.sub.f(x) is above body temperature (37.degree. C.) at any
location along the predetermined length L and increases or
decreases monotonically as a function of x. Thus, the endovascular
device 100 is configured for gradual deployment after delivery and
placement in the body vessel.
[0013] Table 1 summarizes the values of A.sub.f(x) as a function of
x for this example, where x has values x.sub.0, x.sub.1, x.sub.2,
x.sub.3, x.sub.4 and L. Generally speaking, the variable austenite
finish temperature may fall in a range from 37.degree.
C.<A.sub.f(x).ltoreq.T.sub.max, where T.sub.max is below a
temperature that may be harmful to body tissue; for example,
T.sub.max may be 60.degree. C. or lower. The exemplary endovascular
device 100 of this example is an anchoring device (e.g., an
induction triggered active anchoring system (ITAAS)) configured to
pierce the vessel wall and then coil up to exert an anchoring
force, as shown schematically in FIG. 2 and described in U.S.
patent application Ser. No. 15/581,980, filed on Apr. 28, 2017,
which is hereby incorporated by reference.
TABLE-US-00001 TABLE 1 Values of A.sub.f(x) for Exemplary
Endovascular Device as a Function of x x A.sub.f(x) x.sub.0
40.degree. C. x.sub.1 42.degree. C. x.sub.2 45.degree. C. x.sub.3
48.degree. C. x.sub.4 50.degree. C. L 60.degree. C.
[0014] It is assumed that the Nitinol structural element 102, once
placed in the body vessel, attains a temperature up to but not
exceeding about 37.degree. C., which is human body temperature.
After placement in the vessel, the Nitinol structural element 102
is heated, preferably in a controlled manner (e.g., at a specified
heating rate), above body temperature in order to effect
deployment. Typically, the heating begins only after the structural
element 102 has reached a predetermined site in the body vessel,
but in some cases heating may begin prior to reaching the
predetermined site, e.g., during delivery. The heating may be
carried out uniformly along the predetermined length L of the
Nitinol structural element 102, such that the temperature is
uniform to within .+-.1.degree. C.
[0015] As the temperature of the Nitinol structural element 102 is
increased and reaches A.sub.f(x) at each location (e.g., x=x.sub.0,
x.sub.1, x.sub.2, x.sub.3, x.sub.4, or L) along the predetermined
length, the endovascular device 100 is gradually deployed. Gradual
deployment occurs as the element 102 recovers a pre-set shape at
each location during the heating. For example, once the temperature
of the element rises from 37.degree. C. to 40.degree. C., the tip
region x.sub.0 of the Nitinol structural element 102 recovers a
pre-set shape. As the heating continues and the temperature of the
element reaches 42.degree. C., the region of the element 102
between the tip region and up to position x.sub.1 recovers a
pre-set shape. With further heating to a temperature of 45.degree.
C., the region of the element 102 between position x.sub.1 and up
to position x.sub.2 recovers a pre-set shape, and so on, as
illustrated in FIG. 1. Ultimately, upon reaching a temperature at
or above a highest value (60.degree. C. in this example) of the
variable austenite finish temperature of the Nitinol structural
element 102, the endovascular device 100 attains a fully deployed
configuration. The heating of the Nitinol structural element 102
may be carried out by an external (ex vivo) or internal heat
source, such as an induction heater or resistive heat source.
[0016] In addition to the variable austenite finish temperature
A.sub.f(x), the Nitinol structural element 102 may also have a
variable austenite start temperature A.sub.s(x) along the
predetermined length that increases or decreases monotonically as a
function of x. The variable austenite start temperature A.sub.s(x)
is preferably above body temperature at any location along the
predetermined length to prevent deployment of the device from being
initiated prematurely. As the temperature of the element reaches
A.sub.s(x) at each location (e.g., x=x.sub.0, x.sub.1, x.sub.2,
x.sub.3, x.sub.4, or L) along the predetermined length, shape
recovery is initiated at that location.
[0017] As generally understood by those skilled in the art,
austenite start temperature (A.sub.s) refers to the temperature at
which a phase transformation to austenite begins upon heating for a
nickel-titanium shape memory alloy, and austenite finish
temperature (A.sub.f) refers to the temperature at which the phase
transformation to austenite concludes. Martensite start temperature
(M.sub.s) refers to the temperature at which a phase transformation
to martensite begins upon cooling for a nickel-titanium shape
memory alloy, and martensite finish temperature (M.sub.f) refers to
the temperature at which the phase transformation to martensite
concludes. Where the adjective "variable" appears in front of one
of these terms, e.g., "variable austenite start [finish]
temperature," the term may be understood to refer to the
temperature at which the phase transformation begins [concludes]
for the nickel-titanium shape memory alloy as a function of x along
the length of the element.
[0018] In order to maintain the deployed configuration of the
endovascular device 100 after completion of the heating (e.g., when
the device has cooled to body temperature), it may be beneficial to
ensure that the martensite start temperature of the Nitinol
structural element 102 is below body temperature. With a martensite
start temperature below body temperature, the shape memory alloy
may remain austenitic (and thus in the deployed configuration)
while deployed in the body, even after the heating is stopped. The
martensite start temperature may also be selected to be below lower
than body temperature, such as below room (ambient)
temperature.
[0019] A method of heat setting a nitinol-based endovascular device
for controlled deployment in a body vessel is set forth below in
reference to FIG. 3, which shows a Nitinol structural element 102
having the form of a Nitinol wire 104 after a simulated heat
treatment. The Nitinol structural element 102 has a first end 102a
and a second end 102b and is secured in a predetermined
configuration 106, which in the example of FIG. 3 is a coiled
shape. The first end 102a of the element 102 that ultimately forms
the center of the coiled shape (or "coil") may be fixed on a
mandrel while ensuring that each loop of the coil is thermally
isolated from adjacent loops. Thermal isolation may be achieved by
incorporating an insulation layer and/or an air gap between the
loops. In this example, the coil is surrounded by air at 22.degree.
C.
[0020] The first end 102a of the Nitinol structural element 102 is
then heated or "heat set", while the second end 102b of the element
102 is not heated. In this example, the first end 102a is heated to
500.degree. C. by a concentrated heat source. During the heating,
the temperature of the Nitinol structural element 102 is increased
along a length (L) thereof by thermal conduction from the first end
102a, producing a (decreasing) temperature gradient between the
first end 102a and the second end 102b, as illustrated in FIG. 3.
As indicated above, an insulation layer and/or air gap may
partially or fully cover the Nitinol structural element 102 along
the length between the first end 102a and the second end 102b
during the heating to provide thermal insulation between adjacent
loops of the coil. The second end 102b of the element 102 may be
actively cooled, e.g., by convective cooling, in order to modulate
the temperature gradient along the length of the element 102. The
heating may occur at a temperature ("heat setting temperature") and
over a time duration sufficient to induce the Nitinol to adopt a
"memory" of the predetermined configuration (coiled shape in this
example) and a variable austenite finish temperature A.sub.f(x)
above body temperature along the length (L) between the first and
second ends 102a,102b, where 0<x.ltoreq.L. The variable
austenite finish temperature A.sub.f(x) monotonically increases or
decreases as a function of x and is above body temperature at any
location along the length L; thus, the endovascular device 100 is
configured for gradual deployment within a body vessel.
[0021] It is recognized that the phase transformation temperatures
of a nickel-titanium alloy, such as the austenite finish
temperature, may be manipulated by altering the level of
disclocations and/or the nickel content in solid solution, that is,
the amount of nickel present in the matrix of the nickel-titanium
alloy. The nickel content of the matrix may be controlled by either
vaporization or traditional precipitation of nickel using a
suitable heat treatment. Both the temperature and the duration of
the heat treatment (e.g., heat setting), may influence the nickel
content of the matrix.
[0022] Typically, heat setting temperatures from about 350.degree.
C. to about 550.degree. C. are employed for the heating. Higher (or
lower) temperatures within this temperature range and/or longer (or
shorter) heat setting time durations may be used to increase or
decrease the phase transformation temperatures. Guidance may be
provided by a time-temperature-transformation (TTT) diagram for
Nitinol, such as that set forth in Drexel et al., "The Effects of
Cold Work and Heat Treatment on the Properties of Nitinol Wire,"
ASME 2007, 2.sup.nd Frontiers in Biomedical Devices Conference.
[0023] The heating of the first end 102a of the element 102 may be
carried out using a concentrated heat source, such as a laser,
resistive heating element or induction heater. After the
predetermined time duration, the heating may be ceased and the
Nitinol structural element 102 may optionally be exposed to a
cooling fluid (e.g., water) to rapidly quench the temperature. As a
consequence of the heat setting, the Nitinol structural element 102
may have, in addition to a variable austenite finish temperature
A.sub.f(x), a variable austenite start temperature A.sub.s(x),
0<x.ltoreq.L, that is also above body temperature. The variable
austenite start temperature A.sub.s(x) may increase or decrease
monotonically as a function of x.
[0024] After heat setting, the Nitinol structural element 102 may
be deformed (e.g., straightened) into a delivery configuration for
introduction into a body vessel. The deformation into the delivery
configuration may occur while the shape memory alloy is in the
martensitic phase. For example, the Nitinol structural element 102
may be cooled to a temperature at or below the martensite finish
temperature, and the element 102 may be readily deformed to the
desired delivery configuration. The Nitinol structural element 102
may remain in the delivery configuration until heated to a
temperature at or above the lowest austenite start temperature
(e.g., A.sub.s(x.sub.0)) of the element, at which point deployment
of the endovascular device 100 may be initiated. As explained
above, the endoluminal medical device 100 deploys fully once heated
at or above the highest austenite finish temperature (e.g.,
A.sub.f(L)), concluding the controlled deployment process.
[0025] Nitinol structural elements (e.g., wire, rod, tubing, strip)
102 suitable for use in the present method may be obtained
commercially from any of various vendors or fabricated from a
nickel-titanium alloy ingot or billet of a suitable composition
using mechanical working (e.g., hot extrusion, cold drawing) and
annealing methods known in the art. The nickel-titanium alloy is
typically equiatomic or near-equiatomic in composition. For
example, the nickel-titanium alloy may comprise from about 50 at. %
Ni to about 52 at. % Ni, and titanium and any incidental impurities
may account for the balance of the alloy. In some cases, the
nickel-titanium alloy may also include a small amount of an
additional alloying element (AAE) (e.g., from about 0.1 at. % AAE
to about 10 at. % AAE) to enhance the superelastic or other
properties of the nickel-titanium alloy. The additional alloying
element may be selected from among B, Al, Cr, Mn, Fe, Co, Cu, Zn,
Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Hf, Ta, W,
Re, Os, Ir, Pt, Au, Hg, TI, Pb, Bi, Po, V, and Mischmetal.
[0026] Although the present invention has been described in
considerable detail with reference to certain embodiments thereof,
other embodiments are possible without departing from the present
invention. The spirit and scope of the appended claims should not
be limited, therefore, to the description of the preferred
embodiments contained herein. All embodiments that come within the
meaning of the claims, either literally or by equivalence, are
intended to be embraced therein.
[0027] Furthermore, the advantages described above are not
necessarily the only advantages of the invention, and it is not
necessarily expected that all of the described advantages will be
achieved with every embodiment of the invention.
* * * * *